1. Field of the Invention
The present invention relates generally to a mobile terminal, and more particularly to a method and apparatus for removing cross modulation (CM) noise in a wireless transceiver of a mobile terminal.
2. Description of the Related Art
Conventionally, a mobile terminal includes a wireless transceiver for transmitting and receiving data using a wireless signal. The wireless transceiver uses a diversity structure with two receivers to increase the reception performance.
In the mobile terminal with the wireless transceiver of the diversity structure, an important factor for determining reception sensitivity is cross modulation (CM) noise. The CM noise is a non-linear component occurring in an active device. The CM noise usually occurs in a low noise amplifier (LNA) and a mixer of the wireless transceiver.
The CM noise will be described in detail with reference to FIGS. 1A, 1B and 1C. A signal is transmitted from a transmitter through an antenna, and simultaneously the transmitted signal is undesirably received at a receiver through a duplexer. FIG. 1A illustrates frequency bands of received and transmitted signals.
As mentioned above, a transmitted signal undesirably received at the receiver is removed by a band pass filter (BPF) or duplexer isolation, etc., such that the transmitted signal of the transmission frequency band remaining in the received signal is abruptly reduced as illustrated in FIG. 1B.
The transmitted signal still remaining in the received signal is modulated with a single tone jammer in band while going through the LNA or mixer, resulting in CM noise as illustrated in FIG. 1C.
Because the transmitted signal undesirably received at a main receiver through the duplexer is conventionally removed by the duplexer isolation and a second BPF, CM noise is reduced in the main receiver.